Solubility of cilostazol in the presence of polyethylene glycol 4000, polyethylene glycol 6000, polyvinylpyrrolidone K30, and poly(1-vinylpyrrolidone-co-vinyl acetate) at different temperatures

The solubilities of cilostazol in aqueous solutions containing polyethylene glycol 4000 (PEG 4000), polyethylene glycol 6000 (PEG 6000), polyvinylpyrrolidone K30 (PVP K30), and poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA) are measured at temperatures ranging from 298.15 to 318.15 K. It increased with the increase in the hydrophilic carrier concentration and temperature. PVP/VA was the most effective polymer to solubilize cilostazol. The transfer Gibbs free energy (Δ tr G °) and enthalpy (Δ tr H °) values were negative, indicating that the transfer of cilostazol from only water to an aqueous hydrophilic polymer solution is spontaneous and energetically favorable. Furthermore, the Δ tr G ° and Δ tr H ° values decreased with the increase in the hydrophilic polymer concentration, indicating that solubilization is more favorable with the increase in the hydrophilic polymer concentrations. In particular, the Δ tr G ° values considerably decreased for PVP/VA compared to PEG 4000, PEG 6000, and PVP K30. This result indicated that PVP/VA is an effective solubilizing additive for developing oral solid formulations of cilostazol.